Field of the Invention
The present invention concerns a system for generating frame sweeping with laser beam, in particular for projecting images, such as images of moving objects on a wide angle image.
It also concerns, among others, the simulation of the visual environment of pilots during their aerial combat training.
This is practised in simulators comprising one or several large diameter spheres (FIG. 1) the internal surface of which constitutes a concave reflector screen 16 with wide angle. A reproduction of the cockpit 15 of a fighter plane, inside which is placed a pilot to be trained, is located at the center of each sphere.
The ground-view a well as the air-view are simulated for example by two images projected onto the sphere and produced by a projection device 14 placed above the cockpit and which comprises two fish-eye type object lenses orientated facing each other.
Images of the targets are obtained by means of projection systems placed above and to the rear of the pilot. Each of them supplies the image of a target and comprises a "light valve" image generator 10, an image transport system and an orientable projection stick 13 comprising a system of adaption and an optical deviator. Two projection systems thus supply two images of targets in good lighting and definition conditions.
A greater number of images is possible by supplying to each generator a video image formed itself from several target images. A separator thus distributes these images on a corresponding number of projection sticks.
Nevertheless, the number of target images remains limited, on the one hand, because of the diminutions, of the luminosity and of the definition of the images, and which are due to the use of the separator, and on the other hand, due to the possible occultation of the sticks between one another and the complication of the adaption and image transport systems towards the sticks. Furthermore, the projection systems through their siting and their bulkiness, reduce the field of visibility of the pilot while this field on the actual plane tends to increase constantly. Therefore, the optimum solution with this type of projection and from the point of view of images quality, seems to be supplied by a single projection system projecting four target images. This number appears nevertheless as being insufficient and seems able to be increased only through the application of novel means.
The aim of the present invention is therefore the simultaneous generation and projection through laser technique, of about ten target images.
This technique already allows the projection of object images represented by a thread-like outline, in shift sweeping, but these images lack realism. They are suitable for advertising displays. The laser beam deviations are obtained by means of two identical standard galvanometers requiring between each other due to their positioning, a combining short focus optical system which destroys the geometry of the laser beam. The target images are full video images, having thus to be resolved at all distances and to maintain, among others, the contrast and the halo absence inherent to a good quality image. They require a frame sweeping and an infinite field depth, which is only possible by means of appropriate deflectors, if possible without combining optics which imposes downstreams a focussing correction.
Deflector systems with rotating multiface mirrors are already known, with a resolution greater than that which is required for the simulation but which are expensive and bulky. Furthermore, their operating is delicate. They require a servo-speed device, a line synchronization and an adaption of the video to the faces geometry.
The systems called "scanners" with high inertia, in which a mirror integral with a soft iron core oscillates in a magnetic field, are systems of which the temporal resolution remains limited. In the conditions of use required, they are too noisy and lack linearity.
The acoustical-optical deviators are characterized by an angular deviation of about 2.degree., which is not enough for a target image, and require to be completed by an image enlargement by means of special optics. Their luminous yield is low and would require more powerful lasers.
Similarly, the crystal and Kerr effect electro-optical deviators have deviation angles of some minutes, which are much too low for generating a target image.
The object of the system according to the invention is the generation and the projection of a laser image, accoriing to an angular field of about ten degrees; with a maximum definition corresponding to at least 256 lines of 256 pixels, without focussing, contrasted, without halo, with a high luminous yield, and this only by putting into operation simple means of low bulkiness and costs.